Pool irradiator with radiation source in a rotating container

ABSTRACT

An irradiator operable with a radiation source under the surface of a pool of water includes a gas filled space within the irradiator and between the irradiation source and various positions in which containers of material are irradiated. The various positions are at preselected distances from the source to allow simultaneous experiments and the gas filled space conserves radiation. The radiation source may be a plurality of rods within tubes arranged circumferentially to one of the containers of material to be irradiated and the containers of material to be irradiated may be rotated during irradiation.

United States Patent Blanche-Fraser et a1. ..250/52 Ransohoff 1 May 23, 1972 [54] POOL IRRADIATOR WITH RADIATION SOURCE IN A ROTATING CONTAINER Primary Examiner-James W. Lawrence Assistant Examiner-D. C. Nelms [72] Inventor. Jackson A. Ransohofl, Bethesda, Md. Attomey su I e Rothweu, Mion, Zinn & Macpeak [73] Assignee: Neutron Products Inc., Dickerson, Md. [221 Filed: May 28, 1969 [57] ABSTRACT An irradiator operable with a radiation source under the sur- [211 App]' 828519 face of a pool of water includes a gas filled space within the irradiator and between the irradiation source and various posi- U.S. 250/52, {ions in containers of material are irradiated. 'Thc va -i- Int. Clt r t t t H011 ous are at preselected distances from the source to 581 of Search ..250/44, 51, 52, 106, 108. allow Simultaneous experiments and the gas n space com i serves radiation. The radiation source may be a plurality of [56] Re m C rods within tubes arranged circumferentially to one of the UNITED STATES PATENTS containers of material to be irradiated and the containers of 4 2 250 9/ 968 A 1 250/106 material to be irradiated may be rotated during irradiation. 3, l l rragon et a 3,417,239 10/1968 6Clains,2DrawingFlgures Patented May 23, 1972 FIG-l GAS DEMINERALIZED WATER INVENTOR 2 JACKSON A. RANSOHOFF POOL IRRADIATOR WITH RADIATION SOURCE IN A ROTATING CONTAINER BACKGROUND OFTHEINVENTlON 1. Field of the Invention This invention relates to improvements in irradiators, and particularly to a unique irradiator construction for use in a pool. The irradiator, which is particularly suitable for research, accommodates multiple irradiations and has gas rather than water in the radiation space between the sources and the material to be irradiated.

2. Prior Art lrradiators are known and research using various irradiators is common and widespread, although frequently expensive and time consuming. In one type of irradiator, the radiation sources are handled and stored well beneath the surface of a pool of water. In conducting irradiation research, probably the most time consuming operations in setting up or preparing the experiment are directed to determining the dose rate within the experimental volume. Thus for each difierent dose rate, as one moves further from the source, the photon spectrum degrades providing another uncertainty.

Another and related problem in experimental or research irradiation is maintaining conditions of irradiation common from one experiment to another, with the factor of human error being the most elusive variable. Another factor in radiation research is time, it being not unusual for a research irradiation to take several hours or even days.

SUMMARY OF INVENTION This invention solves the problems outlined above by providing means for spacing irradiation positions at various distances from the radiation sources beneath the surface of a pool, and further providing for the space between radiation sources and the material to be irradiated is occupied not by water but by gas. The activity distribution of the sources may be shaped, as previously known in the art, to provide uniformity of dose in the vertical direction. In the horizontal plane the dose rate varies with distance from the sources, so that several experiments at different dose rates can be conducted simultaneously under the same conditions.

The research irradiator for accomplishing these results includes an inverted box with its bottom side open, the box being submerged in a pool. The box has a plurality of radiation source receiving tubes in a circle for receiving source rods and these tubes surround a tube capable of receiving a can containing material to be irradiated. The can may be rotated during irradiation. Other tubes for material to be irradiated extend vertically through the box at predetermined positions spaced from the circle of the source rods so that simultaneous experiments may be conducted. Cans placed within the other tubes may also be rotated to achieve better uniformity of dose. The space beneath the top of the inverted box is filled with a gas, preferably an inert gas such as helium or argon, and this gas displaces the water under the box allowing much more efficient utilization of radiation than if the radiation had to pass through water. The radiation sources can be easily handled while under the water in the pool, and may, at the convenience of the experimentor be moved from one location to another in the source receiving tubes.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a top plan view of the research irradiator of this invention;

FIG. 2 is a sectional elevation taken along line 2-2 of FIG. 1 showing the research irradiator in its position resting on the bottom of the pool and showing the connection for inert gas for displacing water in the radiation space and other connections for rotating a can of material to be irradiated.

2 DESCRIPTION OF THE PREFERRED EMBODIMENT A research irradiator 10 is submerged in a pool 12 of demineralized water a predetermined safe distance beneath the surface, e.g., a minimum of 8 feet below the surface. The pool 12 has a bottom 14, sides 16 and a top deck or ledge 18.

The research irradiator 10 is in the form of an inverted receptacle or box 20 having a top wall 22, side walls 24 but open at the bottom. The receptacle is supported by a framework 26 on legs 28 resting on the pool bottom 14 and is held down by weights 30 or other suitable means.

A radiation source receiver means 32 includes a plurality of tubes 34 arranged in a circle for receiving rods of irradiation source such as coba1t60. As shown in FIG. 1, there may be 36 tubes and the rods of cobalt-60 may be placed in any number of the tubes provided that the irradiation can is rotated, the sources may be either grouped or spaced. If the can is not to be rotated, the sources are preferably spaced equidistantly around the circle.

The radiation source tubes 34 surround a larger tube 38 extending vertically through the receptacle 20 for receiving a sealed container or can 40 containing material M to be irradiated. The can is supported in the tube 38 on a suitable thrust bearing 42 and may be driven in a rotatable manner for rotation about its longitudinal axis by means of a drive flange 44 connected by either a rod or flexible drive cable 46 to a motor drive 48 on the ledge 18. Alternatively, a submerged motor 50 may be utilized to rotate the can 40.

Within the space defined by the top and side walls of th receptacle 20, there are other tubes 52, 54, and 56, 58, etc. These tubes are also for receiving cansof material to be irradiated, not shown, and the cans may be driven similar to can 40. Tubes 52 and 54 are the same distance from the center of the circle defined by the source rods 36 as are tubes 56 and 58. The nearer tubes 52 and 54 are spaced as shown in FIG. 1 so as not to block or interfere with radiation to the more remote tubes 56 and 58. Other tubes 59, 61, 63, 65 and 67 are also similarly situated to allow direct access to the radiation source. Thus, simultaneous experiments can be performed under the same conditions.

In order to provide an inert gas in the radiation space defined by the top and side walls of receptacle 20, there is a source of gas, preferably inert under pressure connected via line 62 and opening 64 to the radiation area. The gas is controlled by valve 66 so that it may be controllably released. The gas under pressure released will rise and create a gas space underneath the top 22 of receptacle 20 and displace the water from this gas space. The gas is released until enough water is displaced to make the radiation space water free. The gas blocks or slows down much less radiation and thus allows a much more eflicient and consistent irradiation of the material in the cans in the material receiving tubes. The gas 10 tends to buoy the receptacle, and to prevent it from floating, suitable weights 30 may be provided.

It is believed that the operation of the irradiator is apparent from the foregoing detailed description but a brief resume will be given. Material M to be irradiated in a research experiment is loaded into a can such as can 40 and sealed and the can is positioned in a tube such as tube 38 of the irradiator. Cobalt-60 rods 36 are loaded into certain preselected tubes 34 to provide the radiation source. Additional cans of any other material to be irradiated in a simultaneous experiment may be loaded into other cans and placed in tubes 52, 54, 56, 58, etc. These tubes are positioned at various distances from the center of the circle of the source rods so as not to block the radiation from the center of the circle as shown in FIG. 1. The cans are rotated either by a motor 48 above the surface of the pool or submerged motor 50 during irradiation.

If dose rate is a variable, multiple irradiations may be performed at different dose rates. If the particular experiment is not dose rate dependent, then, simultaneous irradiations at difierent dose rates will develop data for several doses over a fixed time period.

Thus irradiator significantly cuts the cost of research irradiation by permitting well controlled simultaneous experiments, while maintaining constant conditions other than radiation dose, and simplifying the handling of the radiation sources and material to be irradiated while maintaining safety conditions. In effect, the facility of providing different dose rates by spacing the experiments from the source which is inherent in an air chamber is, by means of the present invention, provided in a water shielded irradiator.

What is claimed is:

1. An irradiator submerged in a pool under a depth of water suitable for safety conditions, the irradiator comprising; a receptacle similar to an inverted box having a top with side walls gas tight and air tight therewith and being open at the bottom, a radiation source that means extending vertically through the top of the receptacle and downward therein, a plurality of tubes extending vertically through the top of the receptacle, each tube receiving a container of material to be irradiated from the top of the pool, the tubes each being at different predetermined distances from the radiation source receiver means, a source of inert gas under pressure, and a controlled fluid connection between the source of inert gas under pressure and the receptacle so that the inert gas may be controllably released to displace water from an irradiation space beneath the top and between the side walls of the receptacle.

2. An irradiator as in claim 1 wherein the radiation source receiver means includes a circle of tubes for receiving radiation source: in the form of rods therein, the radiation source tubes surrounding one of the tubes for receiving a container of material to be irradiated.

3. An irradiator as in claim 1 wherein the receptacle is rectangular in plan and all of the material receiving tubes are spaced so that one does not shield the other from radiation emanating from the radiation source receiver means.

4. An irradiator as in claim 1 further comprising a motor above the surface of the pool, a drive mechanism connecting the motor to a container of material to be irradiated positioned within one of the material receiving tubes for rotating the container while the container is in the receiving tube.

5. An irradiator as in claim 1 further comprising a motor submerged in the pool below the open bottom of the receptacle, the motor being directly connected for driving a container of the material to be irradiated while the container is positioned in one of the container receiving tubes.

6. An irradiator as in claim 1 wherein the receptacle has legs which rest on the bottom of the pool and the receptacle is weighted to overcome the buoyancy created by inert gas in the radiation space. 

1. An irradiator submerged in a pool under a depth of water suitable for safety conditions, the irradiator comprising; a receptacle similar to an inverted box having a top with side walls gas tight and air tight therewith and being open at the bottom, a radiation source that means extending vertically through the top of the receptacle and downward therein, a plurality of tubes extending vertically through the top of the receptacle, each tube receiving a container of material to be irradiated from the top of the pool, the tubes each being at different predetermined distances from the radiation source receiver means, a source of inert gas under pressure, and a controlled fluid connection between the source of inert gas under pressure and the receptacle so that the inert gas may be controllably released to displace water from an irradiation space beneath the top and between the side walls of the receptacle.
 2. An irradiator as in claim 1 wherein the radiation source receiver means includes a circle of tubes for receiving radiation sources in the form of rods therein, the radiation source tubes surrounding one of the tubes for receiving a container of material to be irradiated.
 3. An irradiator as in claim 1 wherein the receptacle is rectangular in plan and all of the material receiving tubes are spaced so that one does not shield the other from radiation emanating from the radiation source receiver means.
 4. An irradiator as in claim 1 further comprising a motor above the surface of the pool, a drive mechanism connecting the motor to a container of material to be irradiated positioned within one of the material receiving tubes for rotating the container while the container is in the receiving tube.
 5. An irradiator as in claim 1 further comprising a motor submerged in the pool below the open bottom of the receptacle, the motor being directly connected for driving a container of the material to be irradiated while the container is positioned in one of the container receiving tubes.
 6. An irradiator as in claim 1 wherein the receptacle has legs which rest on the bottom of the pool and the receptacle is weighted to overcome the buoyancy created by inert gas in the radiation space. 